Title:
The expanding bipolar shell of the helium nova V445 Puppis

Abstract: From multi-epoch adaptive optics imaging and integral field unit spectroscopy
we report the discovery of an expanding and narrowly confined bipolar shell
surrounding the helium nova V445 Puppis (Nova Puppis 2000). An equatorial dust
disc obscures the nova remnant, and the outflow is characterised by a large
polar outflow velocity of 6720 +/- 650 km/s and knots moving at even larger
velocities of 8450 +/- 570 km/s. We derive an expansion parallax distance of
8.2 +/- 0.5 kpc and deduce a pre-outburst luminosity of the underlying binary
of log L/L_Sun = 4.34 +/- 0.36. The derived luminosity suggests that V445
Puppis probably contains a massive white dwarf accreting at high rate from a
helium star companion making it part of a population of binary stars that
potentially lead to supernova Ia explosions due to accumulation of helium-rich
material on the surface of a massive white dwarf.